The key motivation for using drilled shafts: economics.
There also may be situations in which drilled shafts are not economically suited to a particular project. For example, where soft clays and/or loose, water-bearing sands to large depths are encountered, the resistance advantage and relative ease of construction afforded by driven piles or other alternates sometimes may make them more economical than drilled shafts. For small, single-span bridges in which the designer requires batter piles in the abutments, driven piles often are more economical than drilled shafts. However, in most other instances, drilled shafts are cost-competitive with driven piles when both systems are designed appropriately.